Electric-cyclonic hot air furnace



Aug. 25, 1970 R. w. sEA'BuRY, JR 3,525,851

ELECTRIC'CYCLONIC HOT AIR FURNACE Filed Dec. 28, 1967 s sheetssixeet 1 Oll 3 0 l 32 "m l 2 HH will l7 5 RICHARD w. suaunr, JR.

3 JNVENTOR.

T BY FIIJMWIMWJIIVIMIIII RNEY United States Patent O U.S. Cl. 219--370 9Claims ABSTRACT OF THE DISCLOSURE A stack of spaced heat transfermembers is disposed within the annular housing of a centrifugal blowerhaving an elongated axial inlet opening and a tangential outlet opening.The heat transfer members have peripheral contours corresponding to theinside contour of the housing and each member carries electricalresistance elements connectable to a source of voltage. A squirrel cagerotor, aligned with the housing inlet opening, extends through aligned,elongated openings formed in the heat transfer ing the electrical powersupplied to the heater elements in proportion to the sum of the ohmicresistance of the two heat sensors, which sensors have dilferentresponse characteristics and operating temperature ranges.

The above-stated and other objects and advantages of the invention willbecome apparent from the following description when taken with theaccompanying drawings showing several modifications of the invention. Itwill be understood, however, that the drawings are for purposes ofillustration and are not to be construed as defining the I scope orlimits of the invention, reference being had for members and the housingis mounted for adjustment relative to the rotor, thereby to controlrecirculation of the cyclonic air stream in the housing.

BACKGROUND or THE INVENTION The invention relates to apparatus forheating and propelling air and more particularly to space heatingapparatus of the class comprising a blower arranged to move air overelectrical heating elements.

Electrical air heaters of various constructions are available but theprior heaters have relatively low operating efiiciency. Consequently,space heating by electricity has been too costly to gain widespread useexcept in'areas of cheap or surplus power or areas having a mild winterclimate. Even in industry, where convenience and other advantages can beafforded, electrical space heating is not specified Where large amountsof make-up air are required in process uses. The construction andarrangement of prior electrical space heaters is such that there isconsiderable inefiiciency in the transfer of the electrical resistancewaste heat to the air stream which is impelled into the space to beheated. In apparatus made in accordance with this invention, the meansfor heating and impelling the air are combined in a single unit and soarranged that the operating efficiency is significantly higher than inapparatus heretofore available.

An object of this invention is the provision of apparatus for heatingair by electrical resistance heat, which apparatus comprises a singleunit for heating and impelling the air, thereby resulting in highoperating efliciency.

, An object of this invention is the provision of electricalspace-heating apparatus wherein the heat-generating elements aredistributed around the rotor of a centrifugal blower. v An object ofthis invention is the provision of space heating apparatus, comprising astack of spaced heat-transfer members disposed within a housing,electrical heat-generating elements carried by each of the members andconnectable to a source of voltage, a squirrel cage rotor passingthrough aligned holes formed in said members and means mounting thehousing for adjustment relative to the rotor thereby to control therecirculation of the air stream within the housing.

An object of this invention is the provision of a space heating systemcomprising a centrifugal type blower having electrical heater elementsdistributed around the rotor,

a heat sensor positioned at the blower outlet and a heat sensorpositioned at a remote point and in the space to be heated, and anelectrical controller connected between the heat sensors and the heaterelements, said controller varythe latter purpose to the claims appendedhereto.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings wherein like referencecharacters denote like parts in the several views;

FIG. 1 is a top plan view of air heating and impelling apparatus made inaccordance with this invention;

FIG. 2 is a side elevational view thereof;

FIG. 3 is a front elevational view thereof;

FIG. 4 is a fragmentary, exploded isometric view showing the heattransfer plates carrying electrical heater elements;

FIG. 5 is a side elevational view showing a heat transfer plate made inaccordance with another embodiment of the invention;

FIG. 6 is a cross-sectional view taken along the line VI-VI of FIG. 5and drawn to an enlarged scale;

FIG. 7 is an end view showing a stacked arrangement of heat transferplates of a different construction; and

FIG. 8 is a circuit diagram of apparatus for controlling the electricalpower supplied to the heater elements.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1-3, thereis shown a centrifugal blower having an annular housing 10 terminatingin a tangential outlet opening 11 and pivotally supported on a base 12by an elongated hinge 13. A conventional, squirrel cage rotor 14 has ashaft 15 rotatable in bearings 16, 16' carried by the spaced, A-framesupports 17, 17 which are bolted to the base. A drive motor 18, securedto the base, has its shaft coupled to the rotor shaft by means ofpulleys and a belt. In a conventional, centrifugal blower, the rotor,having an axial length substantially equal to the width of the housing,is in alignment with two circular openings formed in the side walls ofthe annular housing 10, said openings having a diameter corresponding tothat of the rotor. These circular openings constitute the axial inlet ofthe blower. Upon rotation of the rotor, air is drawn into the housingthrough these openings and is impelled out of the tangential outletopening 11. In accordance with this invention, the two inlet openingsare of generally oval shape as shown by the dotted line 19 in FIG. 2,thereby to afford a certain amount of angular displacement of thehousing 10 about the axis of the hinge 13 and relative to the fixedposition of the rotor. When the housing is in the position shown in FIG.2, the rotor is disposed close to the short radius wall 20 of thehousing, thereby resulting in a minimum recirculation of the cyclonicair stream around the annular housing. When the housing is rotated in acounter-clockwise direction, as viewed in FIG. 2, the rotor ispositioned further away from such housing wall, thereby resulting inincreased recirculation of the internal air stream.

The angular adjustment of the blower housing, for purposes which will beexplained hereinbelow, can be effected manually or automatically. Amotor 22 has its housing pivotally connected to a bracket 23, secured tothe base, and its drive shaft connected to a partially- 3 threaded rod24. The threaded, lower portion of the rod passes through a threadedhole formed in the upper end of a generally U-shaped bracket which issecured to the motor housing. The upper portion of this rod passesthrough an elongated slot formed inan L-shaped bracket 26 which issecured to the annular housing 10. A pair of bushings 27 are disposed onopposite sides of the bracket 26 and are secured 'to the rod, as by setscrews. It will be apparent that the housing can be displaced, relativeto the rotor, either by rotation of the handle 28 or by energizing themotor 22 from a remote point. A pair of flat, oval shaped baflle plates30, 30' are secure-d in fixed positions to the respective A-framesupports 17, 17' and overlie the two oval openings formed in the sidewalls of the blower housing. Formed in each baflle plate is a circularopening corresponding to the diameter of the rotor. In the drawings, thebaffle plates are shown spaced somewhat from the housing side walls forclarity of disclosure. In the apparatus, these plates are in flushengagement with the side walls thereby to effectively close-off thoseportions of the oval openings which are not in alignment with the rotor,through-out the range of angular adjustment of the blower housing.Disposed within the blower is a stack of spaced heat-transfer membershaving peripheral contours matching the inside contour of the blowerhousing, the forward ends of such plates 31 being visible in the frontelevational view of FIG. 3. These plates are secured in fixed positionby means of three threaded stacking rods 32-34 and nuts 35-37.

Reference now is made to FIG. 4 showing three of the heat-transferplates 31, said plates having formed therein aligned, openings 38,corresponding in shape and size to the oval openings which are formed inthe side walls of the blower housing. These plates may be made of anysuitable material which is an electrical insulator, a good heatconductor and capable of withstanding the maximum temperature for whicha particular air heater is designed. Preferably, the plates are made ofenamelers steel having a vitreous coating fired onto both surfacesthereof. Fired onto the surfaces of these coatings are resistiveconductive paths having a predetermined pattern. Specifically, theconductive paths have a maximum cross-sectional area in the region wherethe peripheral surface of the plate is of the larger radius and aminimum cross-sectional area where such surface is of the smallerradius. Referring to the threaded stacking rod 33 (see also FIG. 3),this rod passes through aligned holes formed in the plates, which holesalso extend through enlarged terminal areas of the conducting paths.Each plate is clampingly secured to the rod by means of front and backnuts and flat, metal washers, only the forward washers 41 and nuts 42being visible in this particular view. Thus, one end of each of theconductive paths is electrically connected to the rod 33. If de sired,an increased spacing of the plates is obtained by metal bushings 43carried by the rods and positioned between adjacent plates. An insulatorbushing 44 and washer 45 are provided for the forward end of the rod,said bushing having a shank which passes through a hole formed in theside wall of the blower housing and said washer being positionable onthe protruding portion of the shank, all for the purpose of electricallyinsulating this end of the rod from the blower housing. A similarinsulator bushing and washer is provided for the other end of the rod.The plates are similarly secured to the stacking rod 32 which rod iselectrically connected to the other ends of the conductive paths and isprovided with insulator bushings and washers as described. These tworods, together with the described metal spacer bushings and fasteningnuts, serve to maintain the plates in a stack formation with a desiredspacing between the plates, and also as terminals for connecting theparallel-connected conductive paths to a source of voltage. The thirdrod 34 also passes through aligned holes formedin the plates and carriesspacer bushings 47 to maintain the plates in a plane substantiallynormal to the axis of the rotor. It will be noted that the conductivepaths are spaced from these bushings and, therefore, the rod 34 need notbe electrically isolated from the blower housing.

Reference now is made to FIGS. 5 and 6 showing a single heat transfermember 50 of a different construction and particularly adapted for usewhen relatively higher output temperatures are required. Here, the heattransfer member 50 comprises a pair of aluminum plates 51 and 52 havingcomplementary, embossed channels 53 and54 formed therein and securedtogether, as by a plurality of rivets 55. An insulated, resistance alloywire 56 is disposed within the matching channels and has ends extendingthrough openings formed at the ends of the channel 53. The insulation isremoved from the projecting ends of the wire and the bare ends areformed into loops, generally concentric with the holes 57 and 58, forelectrical connection to the two stacking rods 32 and 33 shown in FIG.4.

Another construction of the heat transfer members is shown in FIG. 7.Here, each of the plates, identified by numeral 60, has offset edgesforming integral flanges 61. These plates preferably are made ofenamelers steel and the both flat surfaces of each plate have vitreouscoatings fired thereon. Fired onto the coatings are conductive pathssuch as the conductive paths shown in FIG. 4. Also, the plates areprovided with aligned oval openings for receiving the rotor and alignedholes for receiving the stacking rods. The flange of each plate extendsaround the entire periphery thereof except at the straight edge thereof,such edge corresponding to that identified by the numeral 62 in FIG. 4.Thus, when a plurality of such plates are secured together in a stackformation, the plate flanges form an enclosure eliminating the need fora separate annular housing. A flat end plate 63, also carrying aconductive path on the inner surface thereof may be positioned at theend of the stack for purposes of appearance.

In an electric air heater and impeller constructed and arranged asherein described, the heat transfer surfaces are placed where the air tobe heated is the most dense by virtue of its being compressed within theannular housing. This greatly contributes to the heat transferefficiency. Water vapor can be introduced at the center of thecylindrical rotor to further condition the air for greater heat transferefliciency. Also, since the heat transfer surfaces are contained withinthe housing, it can be appreciated that control of air recirculationwithin the housing, by means of the described variable adjustment of thehousing relative to the rotor, provides a wide range of adjustment ofthe percent output air volume, thereby to effect a greater heat transferto meet specific conditions, such as changing input air temperature anda variable air volume output to match an increasing gradient heat lossas measured by an outdoor heat sensor.

The construction and configuration of the heat transfer surfaces willvary with the output temperature desired and the heater will vary insize with the volume of air required and the B.t.u. output. One heatermade in accordance with this invention has an overall size ofapproximately l /2 cubic feet, a 90,000 B.t.u. output rating and a 1500cubic feet per minute volume at 150 F. controlled air. Such unit had atotal heat transfer surface of more than square feet. The large heattransfer area of the unit, positioned in the dense air stream, permitsoperation ofthe heat-generating elements at a relatively low power levelso that the maximum temperatures of these elements is about F. Incontrast, systems having small heat transfer areas, such as hot wiregrids positioned in an air duct, require the generation of high heatlevels, and at such heat levels contaminants in the air stream produceobjectionable odors.

.A further substantial reduction of the electrical power required by aheater made as herein described is achieved by controlling thepowersupplied to the heater elements by a proportional type controllerrather than by an onoif thermostat. A conventional proportional controlcircuit is shown in FIG. 8 to which reference now is made. In thiscircuit, the numeral 65 identifies a 115 volt, AC. voltage source towhich the circuit is connected upon closure of the line switch 66. Twosilicon controlled rectifiers 67 and 68 are connected as full waverectifiers between the voltage source and the resistive load 69, whichload represents the parallel-connected electrical heater elementscarried by the heat-transfer plates and disposed within theblowerhousing. These rectifiers operate as phasecontrolled switches and aremounted on a suitable heat sink to form a separate unit 64, which unitpreferably is positioned in the air stream entering the centrifugalblower. For example, the heat sink may include a suitable mountingbracket provided with two holes whereby the sink can be secured to thesupport 17 (FIG. 2) by means of the bearing mounting bolts. The othercomponents of the control circuit, enclosed within the dotted lines 70,are contained within a suitable housing which can be placed at anyconvenient location.

The firing of the silicon controlled rectifiers 67 and 68 is controlledby the output pulses of a unijunction transistor 71 connected to avariable gain amplifier comprising the transistor 72 which controls thecharging of the capacitor 73. The transistor 72 has its input electrodesconnected across the output diagonals of a four-arm bridge comprisingthefixed resistors 75, 76, the variable resistors 77, 78 and two,series-connected thermistors 80 and 81. The bridge is compensated forambient temperature changes by a compensating resistor 82 and a fixedresistor 83 connected across the bridge arm 76. It is here pointed outthat the thermistor 80 is mounted at the outlet of the blower, whereasthe thermistor 81 is mounted at a remote point in the room being heated.

The thermistors 80 and 81 are selected to provide predetermined changesin ohmic-resistance over temperature ranges of 100-200 F. and 50-80 F.,respectively. Generally, the thermistors are selected to allow automaticincrease or decrease in the controlled heater output temperature ofapproximately 220 F. in opposition to a 110 F. rise or fall in the roomtemperature. Under selected temperatur e conditions, at the twothermistors these thermistors will have a known total resistance, andthe bridge resistors 77 and 78 are adjusted to provide a balancedcondition of the bridge under these conditions. Upon a decrease in thetemperature at the room thermistor 81, its resistance increases therebyunbalancing the bridge in a direction such that the voltage at the baseof the transistor 72 decreases, causing more base and collector currentto flow. This charges up the capacitor 73 more quickly and theunijunction transistor 71 will fire the silicon controlled rectifiersearier in each cycle of the AC. voltage wave, thereby increasing thepower supplied to the heater elements. Increasing power is applied tothe heater elements until the total resistance of the two thermistors isequal to that at which the bridge was balanced. Thus, the controlcircuit supplies only the exact amount of electrical power to the heaterelements to maintain a given output air temperature and to vary suchtemperature bet-ween a high and low limit in proportion to the amountthe room temperature is below the temperature desired, as maybe due tovariable heat load or variable heat loss. Two safety switches 84 and 85are mounted on one of the heat transfer plates contained within theblower. The switch 84'is a thermal actuated, normally-open switch whichturns on the rotor motor 18 when heat is being supplied to the room, andthe switch 85 is a normally-closed, over temperature switch which opensone of the power leads to shut down the entire system if a failureoccurs in the temperature sensing circuit or if the rotor fails torotate.

Having now described the invention, those skilled in this art will beable to make various changes and modifications without thereby departingfrom the scope and spirit of the invention as set forth in the followingclaims.

What is claimed is:

1. Air heating an impelling apparatus comprising,

(a) a generally annular housing having an elongated axial inlet openingand a tangential outlet opening,

(b) a stack of spaced heat transfer members disposed within the housingand having formed therein elongated openings aligned with the said inletopening,

(c) an electrical resistance element carried by each of said members,

(d) means for connecting all of the electrical resistance elements to avoltage source,

(e) an air impelling rotor aligned with said inlet opening and extendingthrough the aligned openings of the heat transfer members, and

(f) means for selectively angularly displacing the housing relative tothe rotor in a plane normal to the rotor axis.

2. The invention as recited in claim 1, wherein the heat transfermembers comprise fiat plateslying in a plane substantially normal to therotor axis, said plates being made of an insulating material and havingperipheral contours corresponding to the inside contour of said housing,and wherein the resistance elements are conductive paths fired onto thesurfaces of each plate.

3. The invention as recited in claim 1, wherein the heat transfermembers comprise metal plates lying in a plane substantially normal tothe rotor axis and having peripheral contours corresponding to theinside contour of said housing, said plates having vitreous coatingsformed thereon, and wherein the resistance elements are conductive pathsfired onto the vitreous coatings.

4. The invention as recited in claim 1, wherein each of the heattransfer members comprises two plates having peripheral contourscorresponding to the inside contour of said housing, said plates havingcomplementar channels formed therein, and wherein the resistance elementis an alloy wire disposed in the channels.

5. The invention as recited in claim 1, wherein the means for connectingthe resistance elements to a voltage source comprises a pair of metalrods extending through aligned holes formed in the heat transfer membersand the side walls of said housing, and means electrically con nectingeach rod to a corresponding end of the resistance elements.

6. The invention as recited in claim 1, in combination with a pair ofresistance-type temperature sensors, one positioned at the outletopening of said housing and the other positioned at a remote point inthe space to be heated, and a proportional type controller having itsinput circuit connected to said temperature sensors and an outputcircuit connected to the resistance elements, said controller varyingthe electrical power supplied to the resistance elements in proportionto changes in the resistance of said sensors.

7. An electrical space heating system comprising,

(a) a centrifugal blower having a generally annular housing having anelongated axial inlet opening and a tangential outlet opening, and asquirrel cage rotor axially-aligned with the inlet opening,

(b) a stack of spaced heat transfer members disposed within the housingand having peripheral contours corresponding to the inside contour ofthe housing, said members lying in a plane normal to the rotor axis andhaving formed therein elongated openings aligned with said inlet openingand through which the said rotor extends,

(c) electrical resistance elements carried by each of the heat transfermembers,

(d) a pair of terminal means connecting all of the resistance elementsin parallel,

(e) means for selectively angularly displacing the housing relative tothe rotor in a plane normal to the rotor axis,

(f) a first thermistor disposed at the said outlet opening and connectedin series with a second thermistor positioned in the space to be heated,

(g) a proportional type electrical control circuit connected between thesaid thermistors and the said terminal means, said circuit supplyingelectrical power to the resistance elements in proportion to changes inthe resistance of the thermistors,

(h) a drive motor coupled to the rotor, and t (i) means energizing saidmotor when power is being supplied to said resistance elements.

8. The invention as recited in claim 7, wherein the said control circuitincludes power rectifiers operated as phase-controlled switches andconnected to the said terminal means, said rectifiers being mounted on aheat sink positioned at the said inlet opening.

9. The invention as recited in claim 7, wherein the heat transfermembers comprise metal plates having a vitreous coating formed on bothsurfaces thereof, wherein the said resistance elements are conductivepaths fired onto the coatings, each such path terminating in ends at thesaid outlet opening, and wherein the said terminal means comprises apair of spaced rods passing through aligned openings formed in the heattransfer members and the housing, each rod being electrically connectedto corresponding ends of the conductive paths.

ANTHONY BARTIS,

References Cited UNITED STATES PATENTS De Mare 219-370 Porzel 219-365 LeGrand 165-122 X Hynes 219-376 X Osterheld 219-376 Sargeaunt 236-91 Quirk219-375 X Pryor 219-369 Broski 219-364 X Primary Examiner US. Cl. X.R.

